Implantable medical devices (IMDs) for cardiac monitoring or for delivering therapy typically include one or more sensors positioned in a patient's blood vessel, heart chamber or other portion of the body. Examples of IMDs include heart monitors, therapy delivery devices, pacemakers, implantable pulse generators (IPGs), pacer-cardio-defibrillators (PCDs), implantable cardio-defibrillators (ICDs), cardiomyo-stimulators, nerve stimulators, gastric stimulators, brain stimulators and drug delivery devices. In a cardiac therapy or monitoring context, such IMDs generally include electrodes for sensing cardiac events of interest and sense amplifiers for recording or filtering sensed events.
In many currently available IMDs, sensed events such as P-waves and R-waves are employed to control the delivery of therapy in accordance with an operating algorithm. Selected electrogram (EGM) signal segments and sense event histogram data and the like are typically stored in IMD RAM for transfer to an external programmer by telemetric means at a later time.
Efforts have also been made to develop implantable physiologic signal transducers and sensors for monitoring a physiologic condition other than, or in addition to, an EGM, to thereby control delivery of a therapy, or to filter or store data. In respect of cardiac monitoring, sensing and recording such additional physiologic signals as blood pressure, blood temperature, pH, blood gas type and blood gas concentration signals has been proposed.
One type of ideal physiologic sensor provides information concerning a patient's exercise level or workload and operates in closed loop fashion. In other words, such an ideal physiologic sensor operates to minimize divergence from an ideal operating point or set of points. Blood oxygen saturation provides a direct indication of the amount oxygen consumed by a patient when exercising. Moreover, in a rate responsive pacing context, oxygen saturation is generally inversely related to pacing rate. That is, as oxygen saturation decreases due to exercise, pacing rates correspondingly increase so that divergence from the optimum operating point is minimized. Thus, development of a reliable, accurate sensor for monitoring blood oxygen saturation for use in conjunction with an IMD is desirable.
Those skilled in the art have therefore toiled for years to develop an implantable oxygen sensor capable of not only accurately and reliably sensing blood oxygen saturation levels, but also of being manufactured easily at a reasonable cost. Such efforts have included attempts to develop systems for recording oxygen saturation and absolute pressure simultaneously, or to initiate or modify therapy on the basis of blood oxygen saturation. The exemplary prior art pertaining to implantable blood oxygen sensors includes the U.S. patents listed in Table 1 below.
Considerable effort has been expended in designing chronically implantable temperature sensors and relative or absolute pressure sensors. Nevertheless, a need still exists for a body implantable, durable, long-lived and low-power-consuming pressure sensor capable of accurately sensing absolute or relative pressure in the body over a period of many years. Likewise, a need still exists for a body implantable, durable, long-lived and low-power-consuming temperature sensor capable of accurately and reliably sensing temperature in the body over a period of many years.
Various medical devices have been developed to receive information from one or more physiologic sensors or transducers. A typical physiologic sensor transduces a measurable parameter of the human body, such as blood pressure, temperature or oxygen saturation for example, into a corresponding electrical signal. A conventional approach to attaching a physiologic sensor to a multiple conductor lead extending from an implantable medical device involves connecting the sensor to at least two conductors provided in the lead.
Connecting two physiologic sensors to an implantable medical device in a conventional manner typically involves connecting the medical device to two multiple conductor leads, with a dedicated lead connected to each of the two sensors. The additional number of leads and associated connection hardware generally complicates the design of the leads and medical device electronics, increases power consumption and the cost of the device, and reduces overall device reliability.
An improved approach to connecting a medical device to two or more physiologic sensors is disclosed in U.S. Pat. No. 5,593,430 issued to Renger. The disclosed approach involves connecting each of the sensors in parallel to a two conductor lead.
Various implementations of systems for sensing blood oxygen and pressure, or for interconnecting one or more physiologic sensors in an implantable medical device are known in the art. Some examples of such sensors may be found in the patents, patent applications or publications listed in Table 1 below. Note that we admit none of the patents, patent applications or publications set forth in Table 1 below as necessarily constituting prior art in respect of the present invention.
TABLE 1 ______________________________________ Issue/Publication Patent/Document No. Inventor(s) Date ______________________________________ H1114 Schweitzer et al. December 1, 1992 B1 4,467,807 Bornzin June 30, 1992 3,746,087 Lavering et al. July 17, 1973 3,847,483 Shaw et al. November 12, 1974 4,114,604 Shaw et al. September 19, 1978 4,202,339 Wirtzfeld et al. May 13, 1980 4,399,820 Wirtzfeld et al. August 23, 1983 4,407,296 Anderson October 4, 1983 4,421,386 Podgorski December 20, 1983 4,444,498 Heinemann April 24, 1984 4,467,807 Bornzin August 28, 1984 4,523,279 Sperinde et al. June 11, 1985 4,554,977 Fussell November 26, 1985 4,623,248 Sperinde November 18, 1986 4,651,741 Passafaro March 24, 1987 4,697,593 Evans et al. October 6, 1987 4,727,879 Liess et al. March 1, 1988 4,730,389 Baudino et al. March 15, 1988 4,730,622 Cohen March 15, 1988 4,750,495 Moore et al. June 14, 1988 4,791,935 Baudino et al. December 20, 1988 4,807,629 Baudino et al. February 28, 1989 4,807,632 Liess et al. February 28, 1989 4,813,421 Baudino et al. March 21, 1989 4,815,469 Cohen et al. March 28, 1989 4,827,933 Koning et al. May 9, 1989 4,830,488 Heinze et al. May 16, 1989 4,877,032 Heinze et al. October 31, 1989 4,903,701 Moore et al. February 27, 1990 4,967,755 Pohndorf November 6, 1990 5,005,573 Buchanan April 9, 1991 5,040,538 Mortazavi August 20, 1991 5,052,388 Sivula et al. October 1, 1991 5,058,586 Heinze October 22, 1991 5,067,960 Grandjean November 26, 1991 5,113,862 Mortazavi May 19, 1992 5,176,138 Thacker January 5, 1993 5,199,428 Obel et al. April 6, 1993 5,267,564 Barcel et al. December 7, 1993 5,275,171 Barcel January 4, 1994 5,312,454 Roline et al. May 17, 1994 5,324,326 Lubin June 28, 1994 5,329,922 Atlee, III July 19, 1994 5,342,406 Thompson August 30, 1994 5,358,519 Grandjean October 25, 1994 5,377,524 Wise et al. January 3, 1995 5,411,532 Mortazavi May 2, 1995 5,438,987 Thacker et al. August 8, 1995 5,490,323 Thacker et al. February 13, 1996 5,535,752 Halperin et al. July 16, 1996 5,564,434 Halperin et al. October 15, 1996 5,556,421 Prutchi et al. September 17, 1996 WO 80/01620 Kraska et al. August 7, 1980 5,593,430 Renger January 14, 1997 5,601,611 Fayram et al. February 11, 1997 5,743,267 Nikolic et al. April 28, 1998 5,758,652 Nikolic et al. June 2, 1998 5,788,647 Eggers August 4, 1998 ______________________________________
All patents listed in Table 1 hereinabove are hereby incorporated by reference herein, each in its respective entirety. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, the Detailed Description of the Various Embodiments, and the Claims set forth below, at least some of the devices and methods disclosed in the patents of listed herein may be modified advantageously in accordance with the teachings of the present invention.